Image processing to perform error diffusion with dots formed based color component values and their sum relative to a threshold

ABSTRACT

Image processing apparatus and image processing method for formation of high quality image by high-speed error diffusion processing by execution of more complicated threshold condition processing in a simple manner. When error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, upon execution of error diffusion processing on a first density component among the plural density components, a threshold value used in the error diffusion processing is determined based on a density value of a second density component, then the error diffusion processing is performed on the first density component based on the determined threshold value, and the result of execution of the error diffusion processing is outputted. Further, upon execution of the error diffusion processing on the second density component among the plural density components, a threshold value used in the error diffusion processing is determined based on a density value of the first density component, then the error diffusion processing is performed on the second density component based on the determined threshold value, and the result of the error diffusion processing is outputted.

This application is a continuation of application Ser. No. 11/370,982, filed Mar. 9, 2006 (pending), which is a division of application Ser. No. 09/993,641, filed Nov. 27, 2001, now U.S. Pat. No. 7,099,046, issued Aug. 29, 2006.

FIELD OF THE INVENTION

The present invention relates to an image processing apparatus and an image processing method, and more particularly, to an image processing apparatus and an image processing method for pseudo-halftoning by performing error diffusion processing on multivalued image density data.

BACKGROUND OF THE INVENTION

Conventionally, the error diffusion method is known as pseudo-halftoning to represent a multivalued image in binary representation (See “An Adaptive Algorithm for Spatial Gray Scale” in Society for Information Display 1975 Symposium Digest of Technical Papers, 1975, pp. 36). According to this method, assuming that a pixel of interest is P and its density is v, densities of adjacent pixels P0 to P3 of the pixel of interest P, v0 to v3, and a threshold value for binarization is T, a binarization error E in the pixel of interest P is distributed by empirically obtained weighting coefficients W0 to W3 into the adjacent pixels P0 to P3 so that a mean density is macroscopically equal to an original image density.

For example, when the value of output binary data is “o”, If v≧T holds, o=1, E=v−Vmax;  (1) If v<T holds, o=0, E=v−Vmin;

(Vmax: maximum density, Vmin: minimum density) v0=v0+E×W0;  (2) v1=v1+E×W1;  (3) v2=v2+E×W2;  (4) v3=v3+E×W3;  (5)

(Example of weighting coefficients: W0= 7/16, W1= 1/16, W2= 5/16, W3= 3/16)

Conventionally, when a multivalued image is outputted by a color ink-jet printer or the like using 4 color inks of cyan (C), magenta (M), yellow (Y) and black (K), the pseudo-halftoning is performed by using the error diffusion method or the like for each color. Regarding each color, the processing provides an excellent visual characteristic, however, regarding overlapped two or more colors, does not always provide such a excellent visual characteristic.

To solve this problem, Japanese Published Unexamined Patent Application Nos. Hei 8-279920 and Hei 11-10918 disclose halftoning to obtain an excellent visual characteristic even in overlapped two or more colors by using the error diffusion method for combination of two or more colors.

Further, Japanese Published Unexamined Patent Application No. Hei 9-139841 discloses similar improvement by performing pseudo-halftoning independently on two or more colors and then correcting output values by the sum of input values.

Especially, to reduce graininess of intermediate density area of color image, it is effective to perform image formation avoiding overlap between cyan (C) component and magenta (M) component, and for this purpose, the following method is employed.

FIG. 24 shows image formation control according to a conventional ink-jet method.

In this figure, image data is multivalue data where each density component (YMCK) of each pixel is represented as 8-bit data (0-255 gray-scale value).

Assuming that densities of C and M components of original image are C and M, densities Ct and Mt of the C and M components of pixel of interest in the multivalue color image are represented as follows. Ct=C+Cerr Mt=M+Merr Cerr and Merr are error-diffused values of the C and M components with respect to the pixel of interest.

As shown in FIG. 24, regarding C and M image formation, 4 types of image formation controls are performed in accordance with the densities of the C and M components of the pixel of interest.

-   1. If the sum of (Ct+Mt) is equal to or less than a threshold value     (Threshold1), i.e., the value belongs to an area (1) in FIG. 24, dot     printing is not performed using C or M inks. -   2. If the sum of (Ct+Mt) is greater than the threshold value     (Threshold1) and the sum of (Ct+Mt) is less than another threshold     value (Threshold2), and Ct>Mt holds, i.e., the value belongs to an     area (2) in FIG. 24, dot printing using only the C ink is performed. -   3. If the sum of (Ct+Mt) is greater than the threshold value     (Threshold1) and the sum of (Ct+Mt) is less than the other threshold     value (Threshold2), and Ct≦Mt holds, i.e., the value belongs to an     area (3) in FIG. 24, dot printing is performed using only the M ink. -   4. If the sum of (Ct+Mt) is equal to or greater than the other     threshold value (Threshold2), i.e., the value belongs to an area (4)     in FIG. 24, dot printing is performed using the C and M inks.

Note that Threshold1<Threshold2 holds.

However, in the above conventional art, as the image formation for the C and M components differs in accordance with the sum of the density values of the C and M components, the image formation control must be simple. If pixels where image data to be processed changes prior near a threshold value are adjacent to each other, a pixel where the C ink and the M ink overlap with each other and a pixel where these inks do not overlap with each other mixedly appear in the narrow area, and as a result, the quality of image formation is degraded.

To prevent the degradation of image quality, more complicated thresholds may be employed. However, the threshold condition processing must be more complicated, and processing time is prolonged.

Further, since the conventional threshold processing must be inevitably simple in the processing based on the sum of the density values of the C and M components, flexible processing cannot be performed without difficulty.

Further, if exclusive error diffusion is to be performed by using the sum of three components including the black (K) component, the processing becomes very complicated as represented in the following code.

Ct=C+Cerr

Mt=M+Merr

Kt=K+Kerr

If(Ct+Mt+Kt>Threshold1)

If(Ct+Mt+Kt<Threshold2)

If(Ct>Mt&&Ct>Kt)

-   -   Print C

Else

If(Mt>Ct&&Mt>Kt)

-   -   Print M

Else

-   -   Print K

Else

-   -   If(Ct+Mt+Kt<Threshold 3)

If(Ct<Mt&&Ct>Kt)

-   -   Print M     -   Print K

Else

If(Mt<Ct&&Mt<Kt)

-   -   Print C     -   Print K

Else

-   -   Print C     -   Print M

Else

-   -   Print C     -   Print M     -   Print K

Further, in the above conventional art, the input multivalued image data is merely binarized by each color component and subjected to the error diffusion processing as the pseudo-halftoning. On the other hand, in accordance with the progress of color image printing technology by the ink-jet method, some ink-jet printers can handle multivalued image data for color image printing by drop modulation or use of same-color thick and thin inks.

Accordingly, it is desirable to apply multivalue error diffusion processing to the above ink-jet printer. However, in the multivalue error diffusion processing, as the threshold condition processing is so complicated, if the processing is applied to an actual printer, the reduction of printing speed is conceivable. For this reason, upon application of the multivalue error diffusion processing to an ink-jet printer to handle multivalued image data, a processing method capable of maintaining a high processing speed is desirable.

Further, as in the case of the above conventional art, in image formation by completely and exclusively arranging C component and M component dots, in an original image having respectively 50% C and M component, all the pixels are filled with C ink dots or M ink dots, ideally, as shown in FIG. 25A. In this state, if C-ink dot positions and M-ink dot positions are relatively shifted from each other for some reason as shown in FIG. 25B, the image has pixels where C-ink dot and M-ink dot overlap with each other (bluish pixels) and blank pixels without dot throughout most of the image.

Accordingly, in printing by an ink-jet printer using a printhead where C-ink nozzles and M-ink nozzles are arrayed in a scan direction of a carriage of the printer, a formed image periodically changes in accordance with the position of the carriage in the scan direction by variation in carriage scan speed or the like, as shown in FIGS. 25A and 25B, and it looks to a human eye that the density of corresponding area periodically changes due to the variation in probability of occurrence of blank pixels. In other words, to a human eye, the printed result appears as a low-quality image.

On the other hand, if C-ink dots and M-ink dots are independently arranged in an image formation, in an original image having respectively 50% C and M components as in the above case, blank pixels, pixels printed only with the C ink, pixels printed only with the M ink, and pixels printed with both the C and M inks are formed respectively at 25% occurrence uniformly in the formed image, ideally, as shown in FIG. 26A.

In the independent arrangement of C-ink dots and M-ink dots, a pixel to be printed only with the C ink may overlap with an adjacent pixel to be printed with the M ink, as shown in FIG. 26B, on the other hand, there is a probability that a pixel to be printed with both the C and M inks is printed with only the C ink or the M ink. Thus, the overall density change is small in comparison with the exclusive arrangement of C-ink and M-ink dots.

Accordingly, it is understood that the exclusive arrangement of C-ink and M-ink dots has a problem that the uniformity of image is degraded from intermediate to high density areas in view of a trade-off between the effect of reduction of graininess in a highlight portion and image formation accuracy. If only the highlight portion is taken into consideration, as respective dots are initially arranged sufficiently away from each other, the degradation of image quality due to shift of dot positions is very little and the advantage of the exclusive arrangement is rather greater.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an image processing apparatus and an image processing method capable of (1) forming a high quality image by performing high-speed error diffusion processing by performing more complicated threshold condition processing in a simple manner; (2) forming a high quality image at a high speed while using multivalue error diffusion processing; and (3) forming a high quality image by performing optimum pixel arrangement in accordance with image density.

According to one aspect of the present invention, the foregoing object is attained by providing an image processing apparatus for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: first determination means for, upon execution of the error diffusion processing on a first density component among the plural density components, determining a threshold value used in the error diffusion processing based on a density value of a second density component; first error diffusion execution means for executing the error diffusion processing on the first density component based on the threshold value determined by the first determination means; first output means for outputting the result of execution of the error diffusion processing by the first error diffusion execution means; second determination means for, upon execution of the error diffusion processing on the second density component among the plural density components, determining a threshold value used in the error diffusion processing based on a density value of the first density component; second error diffusion execution means for performing the error diffusion processing on the second density component based on the threshold value determined by the second determination means; and second output means for outputting the result of execution of the error diffusion processing by the second error diffusion execution means.

It is preferable that the first and second determination means use a table showing a relation between density and threshold values, for determining the threshold values.

It may be arranged such that the first and second determination means respectively determine plural threshold values for N-ary conversion as well as binarization. In this case, it is preferable that the first and second determination means respectively use plural tables for determining the plural threshold values.

Further, it may be arranged such that the apparatus further comprises: third determination means for, upon execution of the error diffusion processing on a third density component among the plural density components, determining a threshold value used in the error diffusion processing based on the sum of the density values of the first and second density components; third error diffusion execution means for executing the error diffusion processing on the third density component based on the threshold value determined by the third determination means; and third output means for outputting the result of execution of the error diffusion processing by the third error diffusion execution means.

In this manner, it is preferable that in a case where the error diffusion processing is performed on the first to third density components, the first determination means determines the threshold value used in the error diffusion processing on the first density component, based on the sum of the density value of the second density component and a density value of the third density component, and the second determination means determines the threshold value used in the error diffusion processing on the second density component, based on the sum of the density value of the first density component and the density value of the third density component.

Note that the plural density components are a yellow component, a magenta component, a cyan component and a black component, and the first density component is the cyan component, the second density component is the magenta component, and the third density component is the black component.

Further, it is preferable that the apparatus further comprises image formation means such as an ink-jet printer for inputting the error diffusion processing results outputted from the first, second and third output means and performing image formation.

It is preferable that the ink-jet printer has an ink-jet printhead that discharges ink by utilizing thermal energy, and the ink-jet printhead has electrothermal transducers for generating the thermal energy to be supplied to the ink.

According to another aspect of the present invention, the foregoing object is attained by providing an image processing method for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: a first determination step of, upon execution of the error diffusion processing on a first density component among the plural density components, determining a threshold value used in the error diffusion processing based on a density value of a second density component; a first error diffusion execution step of executing the error diffusion processing on the first density component based on the threshold value determined at the first determination step; a first output step of outputting the result of execution of the error diffusion processing at the first error diffusion execution step; a second determination step of, upon execution of the error diffusion processing on the second density component among the plural density components, determining a threshold value used in the error diffusion processing based on a density value of the first density component; a second error diffusion execution step of performing the error diffusion processing on the second density component based on the threshold value determined at the second determination step; and a second output step of outputting the result of execution of the error diffusion processing at the second error diffusion execution step.

According to still another aspect of the present invention, the foregoing object is attained by providing a computer readable storage medium for storing a program for executing the above image processing method.

In accordance with the present invention as described above, when error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, upon execution of the error diffusion processing on the first density component among the plural density components, a threshold value to be used in the error diffusion processing is determined based on the density value of the second density component, then the error diffusion processing is executed on the first density component based on the determined threshold value, and the result of execution of the processing is outputted. Further, upon execution of the error diffusion processing on the second density component among the plural density components, a threshold value to be used in the error diffusion processing is determined based on the density value of the first density component, then the error diffusion processing is executed on the second density component based on the determined threshold value, and the result of execution of the processing is outputted.

According to still another aspect of the present invention, the foregoing object is attained by providing an image processing apparatus for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: calculation means for calculating the sum and difference between density values of the first density component and second density component among the plural density components; M-ary conversion means for converting the sum value into M-ary code by using a first function based on the sum; N-value conversion means for converting the difference value into N-ary code by using a second function based on the difference; and execution means for executing multivalue error diffusion processing respectively on the first and second density components, based on the result of conversion by the M-ary conversion means and the result of conversion by the N-ary conversion means.

Note that M and N are respectively a positive integer equal to or greater than 3.

Further, it is preferable that the first function used in the M-ary conversion means is represented in a first table showing a relation between the sum value and an M-ary code, and the second function used in the N-ary conversion means is represented in a second table showing a relation between the difference value and an N-ary code.

Further, it is preferable that the multivalue error diffusion processing is executed by the execution means by using a two-dimensional table with the result of the conversion by the M-ary conversion means and the result of the conversion by the N-ary conversion means as functions. It may be arranged such that the two-dimensional table is a common table for the first and second density components, otherwise, the two-dimensional table is prepared respectively for the first and second density components.

In the above case, the plural density components are a yellow component, a magenta component, a cyan component and a black component, and the first density component is the cyan component, and the second density component is the magenta component.

Further, it is preferable that the apparatus further comprises image formation means such as an ink-jet printer for inputting the error diffusion processing results and performing image formation.

It is preferable that the ink-jet printer has an ink-jet printhead that discharges ink by utilizing thermal energy, and the ink-jet printhead has electrothermal transducers for generating the thermal energy to be supplied to the ink.

According to still another aspect of the present invention, the foregoing object is attained by providing an image processing method for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: a calculation step of calculating the sum and difference between density values of first density component and second density component among the plural density components; an M-ary conversion step of converting the sum value into M-ary code by using a first function based on the sum; an N-ary conversion step of converting the difference value into N-ary code by using a second function based on the difference; and an execution step of executing multivalue error diffusion processing respectively on the first and second density components, based on the result of conversion at the M-ary conversion step and the result of conversion at the N-ary conversion step.

According to still another aspect of the present invention, the foregoing object is attained by providing a computer readable storage medium for storing a program for executing the above image processing method.

In accordance with the present invention as described above, when error diffusion processing is performed on multivalued image data having plural density components and the result of the error diffusion processing is outputted, the sum and the difference between the density value of the first density component and that of the second density component among the plural density components are calculated, the sum value is converted into M-ary code by using the first function based on the sum, while the difference value is converted into N-ary code by using the second function based on the difference. Then multivalue error diffusion processing is performed on the first density component and the second density component based on the results of the M-ary conversion and the N-ary conversion.

According to still another aspect of the present invention, the foregoing object is attained by providing an image processing apparatus for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: analysis means for examining density values of a first density component and a second density component among the plural density components; and control means for exclusively or independently outputting the result of the error diffusion processing on the first density component and that of the error diffusion processing on the second density component, in accordance with the result of analysis by the analysis means, wherein if at least one of the first and second density components has an intermediate density value, the control means independently outputs the results of the error diffusion processing, while if the first and second density components do not have an intermediate density value, exclusively outputs the results of the error diffusion processing.

It may be arranged such that the analysis means includes: first comparison means for comparing the sum of the density values of the first and second density components among the plural density components with a predetermined threshold value; and second comparison means for comparing the density value of the first density component and the density value of the second density component with each other, and that the control means performs printing by the error diffusion processing based on the first density component or the second density component, based on the results of comparison by the first and second comparison means.

Further, it is preferable that the apparatus further comprises third comparison means for comparing the density value of the first density component with the predetermined threshold value, and the control means further determines whether or not printing by the error diffusion processing is to be performed not only based on the first density component, but also based on the result of comparison by the third comparison means.

Otherwise, it is preferable that the apparatus further comprises fourth comparison means for comparing the density value of the second density component with the predetermined threshold value, and the control means further determines whether or not printing by the error diffusion processing is to be performed not only based on the second density component, but also based on the result of comparison by the fourth comparison means.

In the above case, the plural density components are a yellow component, a magenta component, a cyan component and a black component, and the first density component is the cyan component, and the second density component is the magenta component.

It may be arranged such that the plural density components of the multivalued image data are respectively binarized by the error diffusion processing, otherwise, the plural density components of the multivalued image data are respectively converted into N-ary code (N≧3 positive integer) by the error diffusion processing. Further, it may be arranged such that the apparatus further comprises a table showing relation between a density value and an N-ary code output value, for the N-ary conversion. It may be arranged such that the table is a common table for the first and second density components, otherwise, the table is prepared respectively for the first and second density components.

Further, it is preferable that the apparatus further comprises image formation means such as an ink-jet printer for inputting the result of execution of the error diffusion processing and performing image formation.

It is preferable that the ink-jet printer has an ink-jet printhead that discharges ink by utilizing thermal energy, and the ink-jet printhead has electrothermal transducers for generating the thermal energy to be supplied to the ink.

Note that the intermediate density is higher than an approximately half level of a maximum density level.

According to still another aspect of the present invention, the foregoing object is attained by providing an image processing method for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: an analysis step of examining density values of a first density component and a second density component among the plural density components; and a control step of exclusively or independently outputting the result of the error diffusion processing on the first density component and that of the error diffusion processing on the second density component, in accordance with the result of analysis at the analysis step, wherein at the control step, if at least one of the first and second density components has an intermediate density value, the results of the error diffusion processing are independently outputted, while if the first and second density components do not have an intermediate density value, the results of the error diffusion processing are exclusively outputted.

According to still another aspect of the present invention, the foregoing object is attained by providing a computer-readable storage medium holding a program for execution of the above-described image processing method.

In accordance with the present invention as described above, when error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, the density value of the first density component and that of the second density component among the plural density components are examined, and in accordance with the result of analysis, the results of error diffusion processing on the first and second density components are exclusively outputted unless the density components of the first and second density component have intermediate densities, otherwise, independently outputted if at least one of the first and second density components has an intermediate density.

The invention is particularly advantageous since the error diffusion processing is performed in consideration of the value of another density component, image formation in consideration of overlap with another component is possible, and a high quality image can be formed.

Further, as the threshold used in the error diffusion processing is determined by using a table, the error diffusion processing can be performed at a high speed by performing more complicated threshold condition processing in a simple manner.

Further, when error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, the sum and difference between the density value of the first density component and that of the second density component among the plural density components are calculated, and the sum value is converted into M-ary code by using the first function based on the sum, while the difference value is converted into N-ary code by using the second function based on the difference. Then based on the results of M-ary and N-ary conversion, the multivalue error diffusion processing is performed on the first and second density components. Accordingly, complicated threshold condition processing accompanying the multivalue error diffusion processing becomes unnecessary due to representing the first and second functions in the form of table, introducing the tables into the multivalue error diffusion processing, and performing the error diffusion processing by referring to these tables. Thus the multivalue error diffusion processing can be performed at a high speed.

Further, when error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, the density value of the first density component and that of the second density component among the plural density components are examined, and in accordance with the result of analysis, the results of error diffusion processing on the first and second density components are exclusively outputted unless the density components of the first or second density component have intermediate densities, otherwise, independently outputted if at least one of the first and second density components has an intermediate density. Accordingly, the graininess from highlight to intermediate density areas in the image can be reduced, and the uniformity of the image can be maintained from the intermediate to high density areas, thus a high quality image can be formed.

Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a block diagram showing a schematic configuration of an information processing system according to a common embodiment of the present invention;

FIG. 2 is a block diagram showing a hardware construction of host device 51 and that of image output device 52 constructing the information processing system;

FIG. 3 is a perspective view of an ink-jet printer IJRA as a typical embodiment of the image output device 52;

FIG. 4 is a block diagram showing a software construction used in the information processing system;

FIG. 5 is a flowchart showing the outline of image processing;

FIG. 6 is a flowchart showing image formation control according to a first embodiment of the present invention;

FIGS. 7A to 7C are diagrams showing threshold conditions used in the first embodiment;

FIGS. 8A to 8C are diagrams showing other threshold conditions used in the first embodiment;

FIGS. 9A to 9D are diagrams showing examples of applicable various threshold conditions;

FIG. 10 is a flowchart showing the image formation control according to a second embodiment of the present invention;

FIGS. 11A to 11C are diagrams showing threshold conditions used in the second embodiment;

FIGS. 12A to 12C are diagrams other threshold conditions used in the second embodiment;

FIG. 13 is a flowchart showing the image formation control according to a third embodiment of the present invention;

FIG. 14 is a flowchart showing the image formation control according to a fourth embodiment of the present invention;

FIG. 15 is a diagram showing threshold conditions used in the fourth embodiment;

FIG. 16 is a flowchart showing the image formation control according to a fifth embodiment of the present invention;

FIG. 17 is a diagram showing threshold conditions used in the fifth embodiment;

FIG. 18 is a diagram showing a two-dimensional common table for C and M components used in the fifth embodiment;

FIGS. 19A to 19B are diagrams showing two-dimensional tables specialized for the C and M components;

FIG. 20 is a flowchart showing the image formation control according to a sixth embodiment of the present invention;

FIG. 21 is a diagram showing threshold conditions used in the sixth embodiment;

FIG. 22 is a flowchart showing the image formation control according to a seventh embodiment of the present invention;

FIG. 23 is a diagram showing threshold conditions used in the seventh embodiment;

FIG. 24 is a diagram showing the image formation control according to the conventional ink-jet method;

FIGS. 25A and 25B are diagrams showing image formation by exclusively arranging the C and M components; and

FIGS. 26A to 26B are diagrams showing image formation by independently arranging the C and M components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.

Common Embodiment

First, the outline of a common information processing system used in the following embodiments, the outline of hardware construction, the outline of software construction and the outline of image processing will be described.

FIG. 1 is a block diagram showing a schematic configuration of the information processing system according to a common embodiment of the present invention.

As shown in FIG. 1, the information processing system has a host device 51 comprising a personal computer or the like, and an image output device 52 comprising a printer or the like, interconnected via a bidirectional interface 53. Driver software 54, to which the present invention is applied, is loaded into a memory of the host device 51.

1. Hardware Construction of Host Device 51 and Image Output Device 52

Next, the hardware construction of the host device 51 and that of the image output device 52 will be described.

FIG. 2 is a block diagram showing the hardware construction of the host device 51 and that of the image output device 52 constructing the information processing system.

As shown in FIG. 2, the host device 51, having a processor 1000 and its peripheral devices, serves as a host device. Further, the image output device 52 has a driving portion including a printhead 3010, a carrier (CR) motor 3011 to drive a carrier to move the printhead 3010, a linefeed motor 3012 to feed paper and the like, and a control circuit 3013.

The processor 1000 of the host device 51 includes an MPU 1001 which controls the overall operation of the host device in accordance with a control program, a bus 1002 which interconnects system constituent elements, a DRAM 1003 for temporarily storing programs executed by the MPU 1001 and data, a bridge 1004 which connects the system bus, the memory bus and the MPU 1001, and a graphic adapter 1005 having a control function to display graphic information on a display device 2001 such as a CRT.

Further, the processor 1000 has an HDD controller 1006 which serves as an interface between the processor and an HDD device 2002, a keyboard controller 1007 which serves as an interface between the processor and a keyboard 2003, and a communication I/F 1008 as a parallel interface for communication between the processor and the image output device 52 according to the IEEE 1284 standards.

Further, the processor 1000 is connected, via the graphic adapter 1005, to the display device 2001 (CRT in this embodiment) which displays graphic information and the like for an operator. Further, the processor 1000 is connected, via respective controllers, to the hard disk drive (HDD) device 2002 as a large capacity storage device holding programs and data and the keyboard 2003.

On the other hand, the control circuit 3013 of the image output device 52 has an MCU 3001, having a control program execution function and a peripheral device control function, which controls the overall operation of the image output device main body 52, a system bus 3002 which interconnects the respective constituent elements of the control circuit, and a gate array (G.A.) 3003 including mechanisms to supply print data to the printhead 3010, to perform memory address decoding, and to generate a control pulse to the carrier motor and the like, as a control circuit.

Further, the control circuit 3013 has a ROM 3004 for storing the control programs executed by the MCU 3001, host print information and the like, a DRAM 3005 for storing various data (image print information, print data to be supplied to the printhead and the like), a communication I/F 3006 as a parallel interface for communication between the control circuit and the host device 51 according to the IEEE 1284 standards, and a head driver 3007 which converts a head print signal outputted from the gate array 3003 into an electric signal to drive the printhead 3010.

Further, the control circuit 3013 has a CR motor driver 3008 which converts the carrier motor control pulse outputted from the gate array 3003 into an electric signal to actually drive the carrier (CR) motor 3011, and an LF motor driver 3009 which converts a linefeed motor control pulse outputted from the MCU 3001 into an electric signal to actually drive the linefeed motor.

Next, a particular structure of the image output device 52 will be described.

FIG. 3 is a perspective view of an ink-jet printer IJRA as a typical embodiment of the image output device 52.

In FIG. 3, a carriage HC is engaged with a spiral groove 5004 of a lead screw 5005 which rotates via drive force transmission gears 5009 to 5011 interlocking with forward/reverse rotation of a driving motor 5013. The carriage HC has a pin (not shown) and it reciprocates in directions indicated by arrows a and b, held by a guide rail 5003. The carriage HC has an ink-jet cartridge IJC which integrally comprises a printhead IJH and an ink tank IT. A paper holding plate 5002 presses a print sheet P against a platen 5000 along the moving direction of the carriage HC. Photocouplers 5007 and 5008 are home position detecting members for checking the existence of lever 5006 of the carriage in this area and changing over the rotational direction of the motor 5013. A support member 5016 supports a cap member 5022 for capping the front surface of the printhead IJH. A suction member 5015 performs suction-recovery of the printhead by sucking the inside of the cap member 5022 via a cap inner opening 5023. Member 5019 allows a cleaning blade 5017 to move in back-and-forth directions. A main body support plate 5018 supports the member 5019 and the cleaning blade 5017. It is apparent that any well-known cleaning blade is applicable to the printer of the embodiment. Numeral 5021 denotes a lever for starting the sucking operation of the suction-recovery. The lever 5021 moves along the movement of a cam 5020 engaged with the carriage HC. A well-known transmission mechanism such as clutch change over controls a drive force from the driving motor.

When the carriage HC is at the home position area, a desired one of these capping, cleaning and suction-recovery is executed at its corresponding position by the lead screw 5005. The timing of any of these processings is not limited to the printer of the embodiment, if a desired processing is performed at a well-known timing.

Note that as described above, the ink tank IT and the printhead IJH may be integrally formed as an exchangeable ink cartridge IJC. Further, it may be arranged such that the ink tank IT and the printhead IJH can be separated, and when ink is exhausted, only the ink tank IT is exchanged for new one.

Further, the control circuit described above with reference to FIG. 2 is included in the ink-jet printer IJRA.

The printhead IJH prints a color image by using at least four color inks of yellow (Y), magenta (M), cyan (C) and black (K) based on multivalued density data of respective YMCK components.

2. Outline of Software Construction and Outline of Image Processing

FIG. 4 is a block diagram showing the software construction used in the above-described information processing system.

As it is understood from FIG. 4, to output print data to the image output device 52, the host device 51 performs image processing by collaborated operation among application software, an operating system and driver software in a layer structure.

In the present embodiment, processings individually depending on the image output devices are handled by device-specific drawing functions 31-1, 31-2, . . . , 31-n, separated from a program for generally executing programs depending on individual implementations of image processing apparatus. Further, the core processing of driver software is independent of the individual image output devices.

A line-segmented image converted into a quantized amount is subjected to image processing by a color characteristic conversion module 33, a halftoning module 34 and the like. Further, a print command generation module 35 adds a command to the data and compresses the data, and delivers the generated data to the image output device 52 via a spooler 22 provided in the OS (Operating System).

As shown in FIG. 4, application software 11 is provided in the layer of application software, and a drawing processing interface 21 which receives a drawing command from the application software 11 and the spooler 22 which delivers the generated image data to the image output device 52 such as an ink-jet printer are provided in the layer of the OS (Operating System).

Then, the device-specific drawing functions 31-1, 31-2, . . . , 31-n holding representation formats specific to the image output devices, the color characteristic conversion module 33 which receives line-segmented image information from the OS and which converts the color representation in the driver to a device-specific color representation, a halftoning module 34 which performs conversion to quantized amounts for representing respective pixel states of the device, and the print command generation module 35 which adds a command to the image output device 52 to the halftoning-processed image data, and outputs the data to the spooler 22, are provided in the layer of driver software.

Next, a particular example of image output from the application software to the image output device 52 will be described with reference to the flowchart of FIG. 5 showing the outline of the image processing together with FIG. 4.

When the application software 11 outputs an image to the image output device 52, first, the application software 11 issues drawing commands to draw character(s), line(s), figure(s), bitmap(s) and the like, through the drawing processing interface 21 of the OS (step S1).

When the drawing commands for constructing an image frame/printing area have been completed (step S2), the OS converts the respective drawing commands in the internal format of the OS into a device-specific representation format (line-segmentation of respective drawing unit information) while calling the device-specific drawing functions 31-1, 31-2, . . . , 31-n inside the driver software (step S3), thereafter, delivers the image information line-segmented from the image frame/printing area to the driver software (step S4).

Inside the driver software, the color characteristic conversion module 33 corrects the color characteristic of the device, and converts the color representation inside the driver software to that specific to the device (step S5), further, the halftoning module 34 performs conversion (halftoning) to a quantized amounts for representing respective pixel states of the device (step S6). Note that the conversion to quantized amount here corresponds to the form of data processed by the image output device 52. If printing by the image output device is performed based on e.g. binary data, binarization is performed, and if printing by the image output device is performed based on multivalue data (for printing by using thick/thin inks and printing by using large-sized and small-sized ink droplets), the data is N-ary-converted.

The details of the halftoning will be described in the subsequent embodiments.

The print command generation module 35 receives quantized (binarized/N-ary-converted) image data (step S7). The print command generation module 35 processes the quantized image information in correspondence with the characteristic of the image output device by different methods. Further, the print command generation module 35 compresses the data and adds a command header to the data (step S8).

Thereafter, the print command generation module 35 forwards the generated data to the spooler 22 provided in the OS (step S9), to output the data to the image output device 52 (step S10).

Note that in the present embodiment, the above-described control method is realized by storing a program according to the flowchart of FIG. 5 into the storage device of the host device 51 and executing the program.

As described above, as the core processing of the driver software is independent of individual image output devices, the distribution of data processing between the driver software and the image output device can be flexibly changed without impairing the construction of the driver software. This is advantageous in view of maintenance and management of the software.

Next, several embodiments using the system according to the above-described common embodiment will be described. In the following embodiments, the details of error diffusion processing performed by the halftoning module 34 will be described.

Note that the error diffusion processing to be described below handles multivalued image data where respective pixels are represented by respectively 8-bit (256 level representation) density data of yellow (Y) component, magenta (M) component, cyan (C) component and black (K) component.

First Embodiment

In this embodiment, error diffusion processing, different from the error diffusion processing of the conventional art, capable of complicated threshold condition processing will be described. The processing handles C and M component multivalued image data.

In the present embodiment, multivalued density data is binarized by the error diffusion processing.

FIG. 6 is a flowchart showing image formation control according to the first embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S10, the density values Ct and Mt of the C and M components of pixel of interest are obtained as in the case of the conventional art. Next, at step S20, a threshold value (C threshold) used in error diffusion of the C component is obtained based on the obtained M component density value Mt. More specifically, in this embodiment, threshold tables as shown in Tables 1 and 2 are prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold tables.

At step S30, the threshold value (C threshold) obtained at step S20 is compared with the density value Ct of the pixel of interest. If Ct≧C threshold holds, the process proceeds to step S40, at which setting is made for printing with C ink. Thereafter, the process proceeds to step S50. On the other hand, if Ct<C threshold holds at step S30, process skips step S40 and proceeds to step S50.

At step S50, a threshold value (M threshold) used in error diffusion of the M component is obtained based on the obtained C component density value Ct. More specifically, in this embodiment, the threshold tables as shown in Tables 1 and 2 are prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold tables.

Accordingly, in this embodiment, both of the threshold tables as shown in Tables 1 and 2 are commonly used for the C component and the M component.

At step S60, the threshold value (M threshold) obtained at step S50 is compared with the density value Mt of the pixel of interest. If Mt≧M threshold holds, the process proceeds to step S70, at which setting is made for printing with M ink. Thereafter, the process ends. On the other hand, if Mt<M threshold holds at step S60, process skips step S70 and the proceeds ends.

Thus, by execution of the above processing, complicated threshold setting can be made only by defining threshold tables having a common format and setting different values in the tables, in the threshold condition processing as shown in FIG. 7A similar to the threshold processing according to the conventional art described in FIG. 24, and further, in the threshold condition processing as shown in FIG. 8A with threshold conditions more complicated than those in FIG. 7A.

Table 1 is a threshold table having threshold conditions corresponding to FIG. 7A, and Table 2, a threshold table having threshold conditions corresponding to FIG. 8A.

TABLE 1 THRESHOLD DENSITY VALUE 0 128 1 127 2 126 3 125 4 124 5 123 6 122 7 121 8 120 9 119 10 118 11 117 12 116 13 115 14 114 15 113 16 112 17 111 18 110 19 109 20 108 21 107 22 106 23 105 24 104 25 103 26 102 27 101 28 100 29 99 30 98 31 97 32 96 33 95 34 94 35 93 36 92 37 91 38 90 39 89 40 88 41 87 42 86 43 85 44 84 45 83 46 82 47 81 48 80 49 79 50 78 51 77 52 76 53 75 54 74 55 73 56 72 57 71 58 70 59 69 60 68 61 67 62 66 63 65 64 64 65 65 66 66 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 77 77 78 78 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 86 87 87 88 88 89 89 90 90 91 91 92 92 93 93 94 94 95 95 96 96 97 97 98 98 99 99 100 100 101 101 102 102 103 103 104 104 105 105 106 106 107 107 108 108 109 109 110 110 111 111 112 112 113 113 114 114 115 115 116 116 117 117 118 118 119 119 120 120 121 121 122 122 123 123 124 124 125 125 126 126 127 127 128 128 129 129 130 130 131 131 132 132 133 133 134 134 135 135 136 136 137 137 138 138 139 139 140 140 141 141 142 142 143 143 144 144 145 145 146 146 147 147 148 148 149 149 150 150 151 151 152 152 153 153 154 154 155 155 156 156 157 157 158 158 159 159 160 160 161 161 162 162 163 163 164 164 165 165 166 166 167 167 168 168 169 169 170 170 171 171 172 172 173 173 174 174 175 175 176 176 177 177 178 178 179 179 180 180 181 181 182 182 183 183 184 184 185 185 186 186 187 187 188 188 189 189 190 190 191 191 192 191 193 190 194 189 195 188 196 187 197 186 198 185 199 184 200 183 201 182 202 181 203 180 204 179 205 178 206 177 207 176 208 175 209 174 210 173 211 172 212 171 213 170 214 169 215 168 216 167 217 166 218 165 219 164 220 163 221 162 222 161 223 160 224 159 225 158 226 157 227 156 228 155 229 154 230 153 231 152 232 151 233 150 234 149 235 148 236 147 237 146 238 145 239 144 240 143 241 142 242 141 243 140 244 139 245 138 246 137 247 136 248 135 249 134 250 133 251 132 252 131 253 130 254 129 255 128

TABLE 2 THRESHOLD DENSITY VALUE 0 128 1 127 2 126 3 125 4 124 5 123 6 122 7 121 8 120 9 119 10 118 11 117 12 116 13 115 14 114 15 113 16 112 17 111 18 110 19 109 20 108 21 107 22 106 23 105 24 104 25 103 26 102 27 101 28 100 29 99 30 98 31 97 32 96 33 95 34 94 35 93 36 92 37 91 38 90 39 89 40 88 41 87 42 86 43 85 44 84 45 83 46 82 47 81 48 80 49 79 50 78 51 77 52 76 53 75 54 74 55 73 56 72 57 71 58 70 59 69 60 68 61 67 62 66 63 65 64 64 65 65 66 66 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 77 77 78 78 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 86 87 87 88 88 89 89 90 90 91 91 92 92 93 93 94 94 95 95 96 96 97 97 98 98 99 99 100 100 101 101 102 102 103 103 104 104 105 105 106 106 107 107 108 108 109 109 110 110 111 111 112 112 113 113 114 114 115 115 116 116 117 117 118 118 119 119 120 120 121 121 122 122 123 123 124 124 125 125 126 126 127 127 128 128 129 128 130 128 131 128 132 128 133 128 134 128 135 128 136 128 137 128 138 128 139 128 140 128 141 128 142 128 143 128 144 128 145 128 146 128 147 128 148 128 149 128 150 128 151 128 152 128 153 128 154 128 155 128 156 128 157 128 158 128 159 128 160 128 161 128 162 128 163 128 164 128 165 128 166 128 167 128 168 128 169 128 170 128 171 128 172 128 173 128 174 128 175 128 176 128 177 128 178 128 179 128 180 128 181 128 182 128 183 128 184 128 185 128 186 128 187 128 188 128 189 128 190 128 191 128 192 128 193 128 194 128 195 128 196 128 197 128 198 128 199 128 200 128 201 128 202 128 203 128 204 128 205 128 206 128 207 128 208 128 209 128 210 128 211 128 212 128 213 128 214 128 215 128 216 128 217 128 218 128 219 128 220 128 221 128 222 128 223 128 224 128 225 128 226 128 227 128 228 128 229 128 230 128 231 128 232 128 233 128 234 128 235 128 236 128 237 128 238 128 239 128 240 128 241 128 242 128 243 128 244 128 245 128 246 128 247 128 248 128 249 128 250 128 251 128 252 128 253 128 254 128 255 128

For example, in a case where the threshold condition processing as shown in FIG. 7A is performed in accordance with the present embodiment, first, at steps S20 to S40, the threshold condition processing as shown in FIG. 7B is performed, then at steps S50 to S70, the threshold condition processing as shown in FIG. 7C is performed.

Similarly, in a case where the threshold condition processing as shown in FIG. 8A is performed in accordance with the present embodiment, first, at steps S20 to S40, the threshold condition processing as shown in FIG. 8B is performed, then at steps S50 to S70, the threshold condition processing as shown in FIG. 8C is performed.

Accordingly, in the above-described embodiment, as the threshold condition processing is performed by using a predetermined format threshold table, even if the threshold conditions are complicated as shown in FIGS. 9A to 9D, the processing can be performed in a simple manner, and as the processing is simple, the complicated threshold condition processing can be performed at a high speed.

Second Embodiment

In the first embodiment, the multivalued density data is binarized by the error diffusion processing; in the present embodiment, multivalued density data is ternarized by the error diffusion processing.

FIG. 10 is a flowchart showing the image formation control according to the second embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S100, the density values Ct and Mt of the C and M components of the pixel of interest are obtained as in the case of the conventional art. Next, at step S110, two threshold values (C threshold1 and C threshold2) used in error diffusion of the C component are obtained based on the obtained M component density value Mt. More specifically, in this embodiment, the threshold tables as shown in Tables 3 to 6 are prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold values are determined by referring to the threshold tables.

At step S120, one of the threshold values (C threshold1) obtained at step S110 is compared with the density value Ct of the pixel of interest. If Ct≧C threshold1 holds, the process proceeds to step S130, at which the other threshold value (C threshold2) obtained at step S110 is compared with the density value Ct of the pixel of interest. If Ct≧C threshold2 holds, the process proceeds to step S140, at which setting is made for printing by discharging large ink droplets using the C ink. Thereafter, the process proceeds to step S160. On the other hand, if Ct<C threshold2 holds at step S130, the process proceeds to step S150, at which setting is made for printing by discharging small ink droplets using the C ink. Thereafter, the process proceeds to step S160.

Further, if Ct<C threshold1 holds at step S120, the process skips steps S130 to S150 and proceeds to step S160.

At step S160, two threshold values (M threshold1 and M threshold2) used in error diffusion of the M component are obtained based on the obtained C component density value Ct. More specifically, in this embodiment, the threshold tables as shown in Tables 3 to 6 are prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold values are determined by referring to the threshold tables.

Accordingly, in this embodiment, the threshold tables in Tables 3 to 6 are commonly used for the C component and the M component.

At step S170, one of the threshold values (M threshold1) obtained at step S160 is compared with the density value Mt of the pixel of interest. If Mt≧M threshold1 holds, the process proceeds to step S180, at which the other threshold value (M threshold2) obtained at step S160 is compared with the density value Mt of the pixel of interest. If Mt≧M threshold2 holds, the process proceeds to step S190, at which setting is made for printing by discharging large ink droplets using the M ink. Then, the process ends. On the other hand, if Mt<M threshold2 holds at step S180, the process proceeds to step S200, at which setting is made for printing by discharging small ink droplets using the M ink. Then the process ends.

On the other hand, if Mt<M threshold1 holds at step S170, the process skips steps S180 to S200 and the process ends.

Thus, by execution of the above processing, complicated threshold setting can easily be made only by defining threshold tables having a common format and setting different values in the tables, in the threshold condition processing as shown in FIG. 11A, and further, in the threshold condition processing as shown in FIG. 12A.

Tables 3 and 4 are threshold tables having threshold conditions corresponding to FIG. 11A, and Tables 5 and 6, threshold tables having threshold conditions corresponding to FIG. 12A.

TABLE 3 THRESHOLD DENSITY VALUE 0 85 1 84 2 83 3 82 4 81 5 80 6 79 7 78 8 77 9 76 10 75 11 74 12 73 13 72 14 71 15 70 16 69 17 68 18 67 19 66 20 65 21 64 22 63 23 62 24 61 25 60 26 59 27 58 28 57 29 56 30 55 31 54 32 53 33 52 34 51 35 50 36 49 37 48 38 47 39 46 40 45 41 44 42 43 43 43 44 44 45 45 46 46 47 47 48 48 49 49 50 50 51 51 52 52 53 53 54 54 55 55 56 56 57 57 58 58 59 59 60 60 61 61 62 62 63 63 64 64 65 65 66 66 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 77 77 78 78 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 84 87 83 88 82 89 81 90 80 91 79 92 78 93 77 94 76 95 75 96 74 97 73 98 72 99 71 100 70 101 69 102 68 103 67 104 66 105 65 106 64 107 63 108 62 109 61 110 60 111 59 112 58 113 57 114 56 115 55 116 54 117 53 118 52 119 51 120 50 121 49 122 48 123 47 124 46 125 45 126 44 127 43 128 43 129 44 130 45 131 46 132 47 133 48 134 49 135 50 136 51 137 52 138 53 139 54 140 55 141 56 142 57 143 58 144 59 145 60 146 61 147 62 148 63 149 64 150 65 151 66 152 67 153 68 154 69 155 70 156 71 157 72 158 73 159 74 160 75 161 76 162 77 163 78 164 79 165 80 166 81 167 82 168 83 169 84 170 85 171 86 172 87 173 88 174 89 175 90 176 91 177 92 178 93 179 94 180 95 181 96 182 97 183 98 184 99 185 100 186 101 187 102 188 103 189 104 190 105 191 106 192 107 193 108 194 109 195 110 196 111 197 112 198 113 199 114 200 115 201 116 202 117 203 118 204 119 205 120 206 121 207 122 208 123 209 124 210 125 211 126 212 127 213 127 214 126 215 125 216 124 217 123 218 122 219 121 220 120 221 119 222 118 223 117 224 116 225 115 226 114 227 113 228 112 229 111 230 110 231 109 232 108 233 107 234 106 235 105 236 104 237 103 238 102 239 101 240 100 241 99 242 98 243 97 244 96 245 95 246 94 247 93 248 92 249 91 250 90 251 89 252 88 253 87 254 86 255 85

TABLE 4 THRESHOLD DENSITY VALUE 0 170 1 169 2 168 3 167 4 166 5 165 6 164 7 163 8 162 9 161 10 160 11 159 12 158 13 157 14 156 15 155 16 154 17 153 18 152 19 151 20 150 21 149 22 148 23 147 24 146 25 145 26 144 27 143 28 142 29 141 30 140 31 139 32 138 33 137 34 136 35 135 36 134 37 133 38 132 39 131 40 130 41 129 42 128 43 128 44 129 45 130 46 131 47 132 48 133 49 134 50 135 51 136 52 137 53 138 54 139 55 140 56 141 57 142 58 143 59 144 60 145 61 146 62 147 63 148 64 149 65 150 66 151 67 152 68 153 69 154 70 155 71 156 72 157 73 158 74 159 75 160 76 161 77 162 78 163 79 164 80 165 81 166 82 167 83 168 84 169 85 170 86 171 87 172 88 173 89 174 90 175 91 176 92 177 93 178 94 179 95 180 96 181 97 182 98 183 99 184 100 185 101 186 102 187 103 188 104 189 105 190 106 191 107 192 108 193 109 194 110 195 111 196 112 197 113 198 114 199 115 200 116 201 117 202 118 203 119 204 120 205 121 206 122 207 123 208 124 209 125 210 126 211 127 212 128 212 129 211 130 210 131 209 132 208 133 207 134 206 135 205 136 204 137 203 138 202 139 201 140 200 141 199 142 198 143 197 144 196 145 195 146 194 147 193 148 192 149 191 150 190 151 189 152 188 153 187 154 186 155 185 156 184 157 183 158 182 159 181 160 180 161 179 162 178 163 177 164 176 165 175 166 174 167 173 168 172 169 171 170 170 171 171 172 172 173 173 174 174 175 175 176 176 177 177 178 178 179 179 180 180 181 181 182 182 183 183 184 184 185 185 186 186 187 187 188 183 189 189 190 190 191 191 192 192 193 193 194 194 195 195 196 196 197 197 198 198 199 199 200 200 201 201 202 202 203 203 204 204 205 205 206 206 207 207 208 208 209 209 210 210 211 211 212 212 213 212 214 211 215 210 216 209 217 208 218 207 219 206 220 205 221 204 222 203 223 202 224 201 225 200 226 199 227 198 228 197 229 196 230 195 231 194 232 193 233 192 234 191 235 190 236 189 237 188 238 187 239 186 240 185 241 184 242 183 243 182 244 181 245 180 246 179 247 178 248 177 249 176 250 175 251 174 252 173 253 172 254 171 255 170

TABLE 5 THRESHOLD DENSITY VALUE 0 85 1 84 2 83 3 82 4 81 5 80 6 79 7 78 8 77 9 76 10 75 11 74 12 73 13 72 14 71 15 70 16 69 17 68 18 67 19 66 20 65 21 64 22 63 23 62 24 61 25 60 26 59 27 58 28 57 29 56 30 55 31 54 32 53 33 52 34 51 35 50 36 49 37 48 38 47 39 46 40 45 41 44 42 43 43 43 44 44 45 45 46 46 47 47 48 48 49 49 50 50 51 51 52 52 53 53 54 54 55 55 56 56 57 57 58 58 59 59 60 60 61 61 62 62 63 63 64 64 65 65 66 66 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 77 77 78 78 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 85 87 85 88 85 89 85 90 85 91 85 92 85 93 85 94 85 95 85 96 85 97 85 98 85 99 85 100 85 101 85 102 85 103 85 104 85 105 85 106 85 107 85 108 85 109 85 110 85 111 85 112 85 113 85 114 85 115 85 116 85 117 85 118 85 119 85 120 85 121 85 122 85 123 85 124 85 125 85 126 85 127 85 128 85 129 85 130 85 131 85 132 85 133 85 134 85 135 85 136 85 137 85 138 85 139 85 140 85 141 85 142 85 143 85 144 85 145 85 146 85 147 85 148 85 149 85 150 85 151 85 152 85 153 85 154 85 155 85 156 85 157 85 158 85 159 85 160 85 161 85 162 85 163 85 164 85 165 85 166 85 167 85 168 85 169 85 170 85 171 85 172 85 173 85 174 85 175 85 176 85 177 85 178 85 179 85 180 85 181 85 182 85 183 85 184 85 185 85 186 85 187 85 188 85 189 85 190 85 191 85 192 85 193 85 194 85 195 85 196 85 197 85 198 85 199 85 200 85 201 85 202 85 203 85 204 85 205 85 206 85 207 85 208 85 209 85 210 85 211 85 212 85 213 85 214 85 215 85 216 85 217 85 218 85 219 85 220 85 221 85 222 85 223 85 224 85 225 85 226 85 227 85 228 85 229 85 230 85 231 85 232 85 233 85 234 85 235 85 236 85 237 85 238 85 239 85 240 85 241 85 242 85 243 85 244 85 245 85 246 85 247 85 248 85 249 85 250 85 251 85 252 85 253 85 254 85 255 85

TABLE 6 THRESHOLD DENSITY VALUE 0 170 1 170 2 170 3 170 4 170 5 170 6 170 7 170 8 170 9 170 10 170 11 170 12 170 13 170 14 170 15 170 16 170 17 170 18 170 19 170 20 170 21 170 22 170 23 170 24 170 25 170 26 170 27 170 28 170 29 170 30 170 31 170 32 170 33 170 34 170 35 170 36 170 37 170 38 170 39 170 40 170 41 170 42 170 43 170 44 170 45 170 46 170 47 170 48 170 49 170 50 170 51 170 52 170 53 170 54 170 55 170 56 170 57 170 58 170 59 170 60 170 61 170 62 170 63 170 64 170 65 170 66 170 67 170 68 170 69 170 70 170 71 170 72 170 73 170 74 170 75 170 76 170 77 170 78 170 79 170 80 170 81 170 82 170 83 170 84 170 85 170 86 170 87 170 88 170 89 170 90 170 91 170 92 170 93 170 94 170 95 170 96 170 97 170 98 170 99 170 100 170 101 170 102 170 103 170 104 170 105 170 106 170 107 170 108 170 109 170 110 170 111 170 112 170 113 170 114 170 115 170 116 170 117 170 118 170 119 170 120 170 121 170 122 170 123 170 124 170 125 170 126 170 127 170 128 170 129 170 130 170 131 170 132 170 133 170 134 170 135 170 136 170 137 170 138 170 139 170 140 170 141 170 142 170 143 170 144 170 145 170 146 170 147 170 148 170 149 170 150 170 151 170 152 170 153 170 154 170 155 170 156 170 157 170 158 170 159 170 160 170 161 170 162 170 163 170 164 170 165 170 166 170 167 170 168 170 169 170 170 170 171 170 172 170 173 170 174 170 175 170 176 170 177 170 178 170 179 170 180 170 181 170 182 170 183 170 184 170 185 170 186 170 187 170 188 170 189 170 190 170 191 170 192 170 193 170 194 170 195 170 196 170 197 170 198 170 199 170 200 170 201 170 202 170 203 170 204 170 205 170 206 170 207 170 208 170 209 170 210 170 211 170 212 170 213 170 214 170 215 170 216 170 217 170 218 170 219 170 220 170 221 170 222 170 223 170 224 170 225 170 226 170 227 170 228 170 229 170 230 170 231 170 232 170 233 170 234 170 235 170 236 170 237 170 238 170 239 170 240 170 241 170 242 170 243 170 244 170 245 170 246 170 247 170 248 170 249 170 250 170 251 170 252 170 253 170 254 170 255 170

For example, in a case where the threshold condition processing as shown in FIG. 11A is performed in accordance with the present embodiment, first, at steps S110 to S150, the threshold condition processing as shown in FIG. 11B is performed, then at steps S160 to S200, the threshold condition processing as shown in FIG. 11C is performed.

Similarly, in a case where the threshold condition processing as shown in FIG. 12A is performed in accordance with the present embodiment, first, at steps S110 to S150, the threshold condition processing as shown in FIG. 12B is performed, then at steps S160 to S200, the threshold condition processing as shown in FIG. 12C is performed. Especially, the threshold conditions shown in FIGS. 12A to 12C are effective for improvement in uniformity of halftone image.

Accordingly, in the above-described embodiment, even in ternarization of multivalued image data, as the threshold condition processing is performed by using a predetermined format threshold table, even if the threshold conditions are complicated, the processing can be performed in a simple manner, and as the processing is simple, the complicated threshold condition processing can be performed at a high speed.

Note that in the present embodiment, only ternarization is handled, however, if the ink-jet printer as the image output device is capable of handling quaternary or quinary representation by using drop modulation and same-color various density ink (e.g. thin cyan ink, thick cyan ink, thin magenta ink and thick magenta ink), threshold tables for multivalue error diffusion processing such as quaternarization or quinarization may be generated.

Third Embodiment

In the first and second embodiments, the C and M components among the multivalued density data are handled; in the present embodiment, the K component in addition to these components is handled.

FIG. 13 is a flowchart showing the image formation control according to the third embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S210, the density values Ct, Mt and Kt of the C, M and K components of pixel of interest are obtained. Next, at step S220, a threshold value (C threshold) used in error diffusion of the C component is obtained based on the obtained M and K component density values Mt and Kt. More specifically, in this embodiment, a threshold table as shown in Table 7 is prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold table.

At step S230, the threshold value (C threshold) obtained at step S220 is compared with the density value Ct of the pixel of interest. If Ct≧C threshold holds, the process proceeds to step S240, at which setting is made for printing with the C ink. Thereafter, the process proceeds to step S250. On the other hand, if Ct<C threshold holds at step S230, process skips step S240 and proceeds to step S250.

At step S250, a threshold value (M threshold) used in error diffusion of the M component is obtained based on the obtained C and K component density values Ct and Kt. More specifically, in this embodiment, a threshold table as shown in Table 7 is prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold table.

At step S260, the threshold value (M threshold) obtained at step S250 is compared with the density value Mt of the pixel of interest. If Mt≧M threshold holds, the process proceeds to step S270, at which setting is made for printing with the M ink. Thereafter, the process proceeds to step S280. On the other hand, if Mt<M threshold holds at step S260, the process skips step S270 and proceeds to step S280.

Further, at step S280, a threshold value (K threshold) used in error diffusion of the K component is obtained based on the obtained C and M component density values Ct and Mt. More specifically, in this embodiment, a threshold table as shown in Table 7 is prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold table.

Accordingly, in this embodiment, the threshold table in Table 7 is commonly used for the C component, the M component and the K component.

At step S290, the threshold value (K threshold) obtained at step S280 is compared with the density value Kt of the pixel of interest. If Kt≧K threshold holds, the process proceeds to step S300, at which setting is made for printing with K ink. Then, the process ends. On the other hand, if Kt<K threshold holds, the process skips step S300 and the process ends.

The code representing the core part of the above processing is as follows.

-   -   Ct=C+Cerr     -   Mt=M+Merr     -   Kt=K+Kerr     -   Cthreshold=C_Threshold_Table[Mt+Kt]     -   If(Ct>=Cthreshold)

Print C

-   -   Mthreshold=M_Threshold_Table[Ct+Kt]     -   If(Mt>=Mthreshold)

Print M

-   -   Kthreshold=M_Threshold_Table[Ct+Mt]     -   If(Kt>=Kthreshold)

Print K

By executing the above processing, the threshold condition processing for three components, which is complicated in the conventional art as explained by using program code, can easily be performed only by defining a threshold table having a common format and setting different values in the threshold table.

Table 7 is a threshold table commonly used for the C, M and K components.

TABLE 7 THRESHOLD DENSITY VALUE 0 128 1 127 2 126 3 125 4 124 5 123 6 122 7 121 8 120 9 119 10 118 11 117 12 116 13 115 14 114 15 113 16 112 17 111 18 110 19 109 20 108 21 107 22 106 23 105 24 104 25 103 26 102 27 101 28 100 29 99 30 98 31 97 32 96 33 95 34 94 35 93 36 92 37 91 38 90 39 89 40 88 41 87 42 86 43 85 44 84 45 83 46 82 47 81 48 80 49 79 50 78 51 77 52 76 53 75 54 74 55 73 56 72 57 71 58 70 59 69 60 68 61 67 62 66 63 65 64 64 65 65 66 66 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 77 77 78 78 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 86 87 87 88 88 89 89 90 90 91 91 92 92 93 93 94 94 95 95 96 96 97 97 98 98 99 99 100 100 101 101 102 102 103 103 104 104 105 105 106 106 107 107 108 108 109 109 110 110 111 111 112 112 113 113 114 114 115 115 116 116 117 117 118 118 119 119 120 120 121 121 122 122 123 123 124 124 125 125 126 126 127 127 128 128 129 128 130 128 131 128 132 128 133 128 134 128 135 128 136 128 137 128 138 128 139 128 140 128 141 128 142 128 143 128 144 128 145 128 146 128 147 128 148 128 149 128 150 128 151 128 152 128 153 128 154 128 155 128 156 128 157 128 158 128 159 128 160 128 161 128 162 128 163 128 164 128 165 128 166 128 167 128 168 128 169 128 170 128 171 128 172 128 173 128 174 128 175 128 176 128 177 128 178 128 179 128 180 128 181 128 182 128 183 128 184 128 185 128 186 128 187 128 188 128 189 128 190 128 191 128 192 128 193 128 194 128 195 128 196 128 197 128 198 128 199 128 200 128 201 128 202 128 203 128 204 128 205 128 206 128 207 128 208 128 209 128 210 128 211 128 212 128 213 128 214 128 215 128 216 128 217 128 218 128 219 128 220 128 221 128 222 128 223 128 224 128 225 128 226 128 227 128 228 128 229 128 230 128 231 128 232 128 233 128 234 128 235 128 236 128 237 128 238 128 239 128 240 128 241 128 242 128 243 128 244 128 245 128 246 128 247 128 248 128 249 128 250 128 251 128 252 128 253 128 254 128 255 128

Accordingly, in the above-described embodiment, as the threshold conditional processing is performed by using a predetermined format threshold table, even the error diffusion processing handling three components with complicated threshold conditions can be performed in a simple manner, and as the processing is simple, the complicated threshold condition processing can be performed at a high speed.

Further, if the present embodiment is combined with the ternarization processing of the second embodiment, the advantages of simplification and increase in processing speed can be further improved.

Note that the present invention is not limited to the threshold tables described in the above-described embodiments. If the format of the threshold table is maintained while the values set in the table are changed, processing can be performed with various threshold conditions as follows.

-   -   (1) instead of the sum of the C and M component density values         (C+M), threshold conditions such as the sum of squares of the C         and M component density values (C²+M²) are employed. Table 8 is         a threshold table used in this case.

TABLE 8 THRESHOLD DENSITY VALUE 0 128 1 127 2 127 3 127 4 127 5 127 6 127 7 127 8 127 9 127 10 127 11 127 12 127 13 127 14 127 15 127 16 126 17 126 18 126 19 126 20 126 21 126 22 126 23 125 24 125 25 125 26 125 27 125 28 124 29 124 30 124 31 124 32 123 33 123 34 123 35 123 36 122 37 122 38 122 39 121 40 121 41 121 42 120 43 120 44 120 45 119 46 119 47 119 48 118 49 118 50 117 51 117 52 116 53 116 54 116 55 115 56 115 57 114 58 114 59 113 60 113 61 112 62 111 63 111 64 110 65 110 66 109 67 109 68 108 69 107 70 107 71 106 72 105 73 105 74 104 75 103 76 102 77 102 78 101 79 100 80 99 81 99 82 98 83 97 84 96 85 95 86 94 87 93 88 92 89 91 90 91 91 91 92 92 93 93 94 94 95 95 96 96 97 97 98 98 99 99 100 100 101 101 102 102 103 103 104 104 105 105 106 106 107 107 108 108 109 109 110 110 111 111 112 112 113 113 114 114 115 115 116 116 117 117 118 118 119 119 120 120 121 121 122 122 123 123 124 124 125 125 126 126 127 127 128 128 129 129 130 130 131 131 132 132 133 133 134 134 135 135 136 136 137 137 138 138 139 139 140 140 141 141 142 142 143 143 144 144 145 145 146 146 147 147 148 148 149 149 150 150 151 151 152 152 153 153 154 154 155 155 156 156 157 157 158 158 159 159 160 160 161 161 162 162 163 163 164 164 165 163 166 163 167 162 168 161 169 160 170 159 171 158 172 157 173 156 174 155 175 155 176 154 177 153 178 152 179 152 180 151 181 150 182 149 183 149 184 148 185 147 186 147 187 146 188 145 189 145 190 144 191 144 192 143 193 143 194 142 195 141 196 141 197 140 198 140 199 139 200 139 201 138 202 138 203 138 204 137 205 137 206 136 207 136 208 135 209 135 210 135 211 134 212 134 213 134 214 133 215 133 216 133 217 132 218 132 219 132 220 131 221 131 222 131 223 131 224 130 225 130 226 130 227 130 228 129 229 129 230 129 231 129 232 129 233 128 234 128 235 128 236 128 237 128 238 128 239 128 240 127 241 127 242 127 243 127 244 127 245 127 246 127 247 127 248 127 249 127 250 127 251 127 252 127 253 127 254 127 255 127

In a case where an ink-jet printer having a slightly greater ink discharge amount is used as the image output device, isolated dots formed by the C or M ink are easily recognized in a very low density image area, and the uniformity of the image is impaired by exclusive arrangement of these dots, if the above threshold conditions are used, the correlation between the C component and the M component can be slightly lowered and the uniformity of the image can be maintained.

-   -   (2) As shown in FIG. 9B, threshold conditions overlapped with         noise are employed. Table 9 is a threshold table used in this         case.

TABLE 9 THRESHOLD DENSITY VALUE 0 130 1 127 2 124 3 125 4 126 5 123 6 120 7 121 8 122 9 119 10 116 11 117 12 116 13 115 14 112 15 113 16 114 17 111 18 108 19 109 20 110 21 107 22 104 23 105 24 106 25 103 26 100 27 101 28 102 29 99 30 96 31 97 32 98 33 95 34 92 35 93 36 94 37 91 38 88 39 89 40 90 41 87 42 84 43 85 44 86 45 83 46 80 47 81 48 82 49 79 50 76 51 77 52 78 53 75 54 72 55 73 56 74 57 71 58 68 59 69 60 70 61 67 62 64 63 65 64 66 65 65 66 64 67 67 68 70 69 69 70 68 71 71 72 74 73 73 74 72 75 75 76 78 77 77 78 76 79 79 80 82 81 81 82 80 83 83 84 86 85 85 86 84 87 87 88 90 89 89 90 88 91 91 92 94 93 93 94 92 95 95 96 98 97 97 98 96 99 99 100 102 101 101 102 100 103 103 104 106 105 105 106 104 107 107 108 110 109 109 110 108 111 111 112 114 113 113 114 112 115 115 116 118 117 117 118 116 119 119 120 122 121 121 122 120 123 123 124 126 125 125 126 124 127 127 128 130 129 129 130 128 131 131 132 134 133 133 134 132 135 135 136 138 137 137 138 136 139 139 140 142 141 141 142 140 143 143 144 146 145 145 146 144 147 147 148 150 149 149 150 148 151 151 152 154 153 153 154 152 155 155 156 158 157 157 158 156 159 159 160 162 161 161 162 160 163 163 164 166 165 165 166 164 167 167 168 170 169 169 170 168 171 171 172 174 173 173 174 172 175 175 176 178 177 177 178 176 179 179 180 182 181 181 182 180 183 183 184 186 185 185 186 184 187 187 188 190 189 189 190 188 191 191 192 193 193 190 194 187 195 188 196 189 197 186 198 183 199 184 200 185 201 182 202 179 203 180 204 181 205 178 206 175 207 176 208 177 209 174 210 171 211 172 212 173 213 170 214 167 215 168 216 169 217 166 218 163 219 164 220 165 221 162 222 159 223 160 224 161 225 158 226 155 227 156 228 157 229 154 230 151 231 152 232 153 233 150 234 147 235 148 236 149 237 146 238 143 239 144 240 145 241 142 242 139 243 140 244 141 245 138 246 135 247 136 248 137 249 134 250 131 251 132 252 133 253 130 254 127 255 128

By using the threshold conditions, the probability of formation of continuous C-ink or M-ink dots can be reduced.

-   -   (3) As shown in FIG. 9C, the tendency of error diffusion is         changed in a highlight area and intermediate to high density         areas. By using the threshold conditions, the degradation of         image quality due to fluctuation of ink dot application position         can be reduced.     -   (4) As shown in FIG. 9D, the boundaries of thresholds are         smoothed as much as possible. By using such threshold         conditions, the abrupt change can be reduced between an area         where C and M inks are exclusively used and an area where the C         and M inks are not exclusively used, and capability of         representing an image can be improved.

In this manner, the threshold condition processing has flexibility by use of a threshold table. If the threshold table is used in combination with actual ink discharge amount or ink composition in the ink-jet printer, the content of image formation processing and/or purpose of the processing can be easily changed.

Fourth Embodiment

Further, assume that the ink-jet printer IJRA can handle multivalued image data by using drop modulation and/or same-color thick and thin inks (e.g., thin cyan ink, thick cyan ink, thin magenta ink and thick magenta ink).

In the present embodiment, unlike the conventional art, multivalued density data is ternarized by the error diffusion processing. The data handled by the error diffusion processing according to this embodiment is C component and M component multivalued image data.

FIG. 14 is a flowchart showing the image formation control according to the fourth embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S310, the density values Ct and Mt of the C and M components of pixel of interest are obtained as in the case of the conventional art. Next, at step S320, it is determined whether or not the sum of the obtained M component density value Mt and the C component density value Ct is greater than a first threshold value (Threshold1). If Ct+Mt>Threshold1 holds, the process proceeds to step S330, at which it is determined whether or not the sum of the M component density value Mt and the C component density value Ct is less than a second threshold value (Threshold2). On the other hand, if Ct+Mt≦Threshold1 holds at step S320, the process ends.

At step S330, if Ct+Mt<Threshold2 holds, the process proceeds to step S340, at which the M component density value Mt and the C component density value Ct are compared with each other. If Ct>Mt holds, the process proceeds to step S350, at which setting is made for printing with small-sized C ink droplet (or thin C ink). On the other hand, if Ct≦Mt holds, the process proceeds to step S360, at which setting is made for printing with small-sized M ink droplet (or thin M ink). After step S350 or S360, the process ends.

At step S330, if Ct+Mt≧Threshold2 holds, the process proceeds to step S370, at which it is determined whether or not the sum of the M component density value Mt and the C component density value Ct is less than a third threshold value (Threshold3). If Ct+Mt<Threshold3 holds, the process proceeds to step S380, at which it is determined whether or not the difference between the M component density value Mt and the C component density value Ct is greater than a predetermined offset value (Offset1). If Ct−Mt>Offset1 holds, the process proceeds to step S390, at which setting is made for printing with large-sized C ink droplet (or thick C ink). Then, the process ends. On the other hand, if Ct−Mt≦Offset1 holds, the process proceeds to step S400.

At step S400, it is determined whether or not the difference between the M component density value Mt and the C component density value Ct is greater than a predetermined offset value (Offset2). If Mt−Ct≦Offset2 holds, the process proceeds to step S410, at which setting is made for printing with small-sized C ink droplet (or thin C ink) and small-sized M ink droplet (or thin M ink). Then, the process ends. On the other hand, if Mt−Ct>Offset2 holds, the process proceeds to step S420, at which setting is made for printing with large-sized M ink droplet (or thick M ink). Then, the process ends.

Further, at step S370, if Ct+Mt≧Threshold3 holds, the process proceeds to step S430, at which it is determined whether or not the sum of the M component density value Mt and the C component density value Ct is less than a fourth threshold value (Threshold4). If Ct+Mt<Threshold4 holds, the process proceeds to step S440, at which the M component density value Mt and the C component density value Ct are compared with each other. If Ct>Mt holds, the process proceeds to step S450, at which setting is made for printing with large-sized C ink droplet (or thick C ink) and small-sized M ink droplet (or thin M ink). Then the process ends. On the other hand, if Ct≦Mt holds, the process proceeds to step S460, at which setting is made for printing with small-sized C ink droplet (or thin C ink) and large-sized M ink droplet (or thick M ink). Then, the process ends.

On the other hand, at step S430, if Ct+Mt≧Threshold4 holds, the process proceeds to step S470, at which setting is made for printing with large-sized C ink droplet (or thick C ink) and large-sized M ink droplet (or thick M ink). Then, the process ends.

FIG. 15 shows the threshold conditions for the C and M components in the processing shown in FIG. 14.

In the above-described processing, the following dot arrangements are made in accordance with the M component density value Mt and the C component density value Ct.

-   -   (1) Ct+Mt≦Threshold1

(C and M components belong to low density area→area (a) in FIG. 15)

Dot printing is not performed.

-   -   (2) Ct+Mt>Threshold1 and Ct+Mt<Threshold2 and Ct>Mt

(C component belongs to intermediate density area→area (b) in FIG. 15)

Dot printing with small-sized C ink droplet (or thin C ink)(exclusive printing).

-   -   (3) Ct+Mt>Threshold1 and Ct+Mt<Threshold2 and Ct≦Mt

(M component belongs to intermediate density area→area (c) in FIG. 15)

Dot printing with small-sized M ink droplet (or thin M ink)(exclusive printing).

-   -   (4) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3         and Ct−Mt>Offset1

(C component belongs to high density area→area (d) in FIG. 15)

Dot printing with large-sized C ink droplet (or thick C ink)(exclusive printing).

-   -   (5) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3         and Ct−Mt≦Offset1 and Mt−Ct≦Offset2

(C and M components belong to intermediate density area→area (e) in FIG. 15)

Dot printing with small-sized C ink droplet (or thin C ink) and small-sized M ink droplet (or thin M ink) (overlay printing).

-   -   (6) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3         and Mt−Ct≦Offset1 and Mt−Ct>Offset2

(M component belongs to high density area→area (f) in FIG. 15)

Dot printing with large-sized M ink droplet (or thick M ink)(exclusive printing).

-   -   (7) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt≧Threshold3         and Ct+Mt<Threshold4 and Ct>Mt

(C component belongs to high density area and M component belongs to intermediate density area→area (g) in FIG. 15)

Dot printing with large-sized C ink droplet (or thick C ink) and small-sized M ink droplet (or thin M ink)(overlay printing).

-   -   (8) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt≧Threshold3         and Ct+Mt<Threshold4 and Ct≦Mt

(C component belongs to intermediate density area and M component belongs to high density area→area (h) in FIG. 15)

Dot printing with small-sized C ink droplet (or thin C ink) and large-sized M ink droplet (or thick M ink) (overlay printing).

-   -   (9) Ct+Mt≧Threshold4         (>Threshold3>Threshold2>Threshold1)

(C and M components belong to high density area→area (i) in FIG. 15)

Dot printing with large-sized C ink droplet (or thick C ink) and large-sized M ink droplet (or thick M ink) (overlay printing).

Accordingly, in the above-described present embodiment, as the printing with the M ink and C ink is changed in accordance with the C component and M component density values, printing with reduced graininess can be performed by ternarizing the C component and M component density values and exclusively arranging printed dots based on the ternarization.

Fifth Embodiment

In the fourth embodiment, the multivalued density data is ternarized by the error diffusion processing; in the present embodiment, an example of high-speed processing in consideration of conversion of multivalued °density data into N-ary code (N≧4) by the error diffusion will be described.

As it is apparent from the flowchart of FIG. 14 described in the first embodiment, in the case of ternarization, the C and M components are respectively ternarized, 9 (=3×3) arrangements are considered and branching processings by 8 “if” statements (condition statements) are required. That is, in the case of converting into N-ary code, N²−1 “if” statements are required. Accordingly, as the value of N increases, processing time increases.

FIG. 16 is a flowchart showing the image formation control according to the fifth embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

In the present embodiment, as the threshold condition processing is very complicated in the conversion of input multivalued image data into N-ary code (N≧3) by the error diffusion processing, the conversion is made by the following procedure.

(1) Functions defined as X=Ct+Mt and Y=Ct−Mt are introduced for execution of multivalue error diffusion.

2) A two-dimensional table is referred to based on the result of multivalue error diffusion processing, so as to determine arrangement of dots to be printed and dot type. The two-dimensional table may be a common table for the C and M components, however, actually, it is preferable that tables (C_Table and M_Table) respectively for the C and M components are prepared.

Returning to FIG. 16, first, at step S510, X and Y values are determined from density values of the C and M components in each pixel.

Next, at step S520, arguments (X_index, Y_index) of the above-described two-dimensional table are determined based on the X and Y values. In this embodiment, the arguments are determined as X and Y functions (X_index=f(X), Y_index=g(Y)).

Finally, at step S530, the two-dimensional table is referred to by using the arguments determined at step S520, and output values by the error diffusion processing of the C and M components (C out, M out) are determined.

For comparison, an example of ternarization processing the same as that described in the fourth embodiment, in accordance with the present embodiment, will be described.

FIG. 17 shows the ternarization according to the fifth embodiment.

FIG. 17 shows quaternarization of X=Ct(=C+Cerr)+Mt(=M+Merr) and quinarization of Y=Ct(=C+Cerr)−Mt(=M+Merr).

In FIG. 17, a right-upward straight line indicates the same X value (=Ct−Mt), and a left-upward straight line, the same Y value (=Ct+Mt) (Ct and Mt have variation widths of about −128≦Ct, Mt≦383 including error accumulation).

Accordingly, as the values Ct and Mt have the above variation widths, the X value has a variation width of about −256≦X≦766, and the Y value, a variation width of about −511≦Y≦511. To quaternarize and quinarize the X and Y values having the above variation widths, the function of X (f(X)) and that of Y (g(Y)) are introduced.

That is, X_index=f(X) and Y_index=g(Y) are calculated. The calculations can be realized by referring to the table.

In this manner, two additions and two multivalue conversion calculations (referring to the table) divide the entire X and Y range into quaternary×quinary=20 sections.

In comparison between FIGS. 17 and 15, the areas (a), (b), (c), (e), (g), (h) and (i) in FIG. 15 are respectively 2 sections in FIG. 17. The entire partitioning is approximately common to FIGS. 15 and 17.

Accordingly, print control based on the error-diffusion processing by C and M ternarization can be performed by referring to a common two-dimensional table as shown in FIG. 18 based on the results of X and Y multivalue conversion.

Note that in FIG. 18, “_” means non-execution of dot printing with C or M ink; “c”, dot printing with small-sized C ink droplet (or thin C ink); “m”, dot printing with small-sized M ink droplet (or thin M ink); “C”, dot printing with large-sized C ink droplet (or thick C ink); “M”, dot printing with large-sized M ink droplet (or thick M ink); “cm”, dot printing with small-sized C ink droplet (or thin C ink) and small-sized M ink droplet (or thin M ink); “Cm”, dot printing with large-sized C ink droplet (or thick C ink) and small-sized M ink droplet (or thin M ink); “cM”, dot printing with small-sized C ink droplet (or thin C ink) and large-sized M ink droplet (or thick M ink); and “CM”, dot printing with large-sized C ink droplet (or thick C ink) and large-sized M ink droplet (or thick M ink).

Actually, it is desirable that two-dimensional tables are prepared respectively for the C and M components in consideration of color characteristics of the C and M components, as shown in FIGS. 19A and 19B.

FIG. 19A shows a two-dimensional table specialized for the C component, and FIG. 19B, a two-dimensional table specialized for the M component.

Further, in FIGS. 19A and B, “_” means non-execution of dot printing; “c”, dot printing with small-sized C ink droplet (or thin C ink); “m”, dot printing with small-sized M ink droplet (or thin M ink); “C”, dot printing with large-sized C ink droplet (or thick C ink); and “M”, dot printing with large-sized M ink droplet (or thick M ink).

In the above example, for the sake of simplification of explanation, ternarization has been described, however, in the present embodiment, as conversion into N-ary code (N≧4) can be realized by using simple processing steps without conditional branch processing, i.e., XY calculation, XY multivalue conversion processing and multivalue conversion of the C and M components, the embodiment provides more effective processing for N of the higher-order.

Accordingly, in the above-described present embodiment, regarding conversion into N-ary code of the higher-order, the error diffusion processing can be performed at a high speed without complicated processing.

Further, according to the above-described present embodiment, as the processing is mainly performed with reference to table(s) without calculation accompanied with condition determination, the processing is advantageous in e.g. pipeline processing and/or lookahead processing used in an MPU such as an Pentium compatible processor. If such processor is employed in the present embodiment, higher-speed processing can be expected.

Sixth Embodiment

In the present embodiment, the error diffusion processing capable of controlling pixel arrangement by each density component in accordance with density value, different from the error diffusion of the conventional art, will be described. The error diffusion processing according to the present embodiment handles multivalued image data of C and M components.

In the present embodiment, the multivalued density data is binarized by the error-diffusion processing.

FIG. 20 is a flowchart showing the image formation control according to the sixth embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S610, the density values Ct and Mt of the C and M components of pixel of interest are obtained as in the case of the conventional art. Next, at step S620, it is determined whether or not the sum of the obtained M component density value Mt and the C component density value Ct is greater than a density value 127 used as a threshold value. If Ct+Mt>127 holds, the process proceeds to step S630, at which the M component density value Mt and the C component density value Ct are compared with each other.

If Ct>Mt holds, the process proceeds to step S640, at which setting is made for printing with the C ink. Further, at step S650, it is determined whether or not the M component density value Mt is greater than the threshold value 127. If Mt>127 holds, the process proceeds to step S670, at which setting is made for printing with the M ink. Then the process ends. On the other hand, if Mt≦127 holds, the process skips step S670 and the process ends.

At step S630, if Ct≦Mt holds, the process proceeds to step S680, at which setting is made for printing with the M ink. Further, the process proceeds to step S690, at which it is determined whether or not the C component density value Ct is greater than the threshold value 127. If Ct>127 holds, the process proceeds to step S700, at which setting is made for printing with the C ink. Then, the process ends. On the other hand, if Ct≦127 holds, the process skips step S700 and the process ends.

Further, at step S620, if Ct+Mt≦127 holds, the process ends.

FIG. 21 is a diagram showing threshold conditions for the C and M components in the processing shown in FIG. 20.

In the above-described processing, the following dot arrangements are made in accordance with the M component density value Mt and the C component density value Ct.

-   -   (1) Ct+Mt≦127

(C and M components belong to low density area→area (a) in FIG. 21)

Dot printing is not performed.

-   -   (2) Ct+Mt>127 and Ct>Mt and Mt>127

(C and M components belong to intermediate to high density area→area (d) in FIG. 21)

Dot printing with C and M inks (overlay printing).

-   -   (3) Ct+Mt>127 and Ct>Mt and Mt≦127

(only C component belongs to intermediate to high density area→area (b) in FIG. 21)

Dot printing with only C ink (exclusive printing).

-   -   (4) Ct+Mt>127 and Ct≦Mt and Ct>127

(C and M components belong to intermediate to high density area→area (d) in FIG. 21)

Dot printing with C and M inks (overlay printing).

-   -   (5) Ct+Mt>127 and Ct≦Mt and Ct≦127

(only M component belongs to intermediate to high density area→area (c) in FIG. 21)

Dot printing with only M ink (exclusive printing).

Accordingly, in the above-described embodiment, if only one density component has a sufficiently high density, printing pixels are formed for the color component without depending on another component. Thus, printing independency of the C and M components in intermediate to high density areas is enhanced. Thus the uniformity of image can be maintained in intermediate and higher density areas.

Seventh Embodiment

In the sixth embodiment, the multivalued density data is binarized by the error diffusion processing; in the present embodiment, multivalued density data is ternarized by the error diffusion processing.

FIG. 22 is a flowchart showing the image formation control according to the seventh embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S710, the density values Ct and Mt of the C and M components of pixel of interest are obtained as in the case of the conventional art. Next, at step S720, the sum of the obtained M component density value Mt and the C component density value Ct is compared with a threshold value (Threshold). If Ct+Mt>Threshold holds, the process proceeds to step S730, while if Ct+Mt≦Threshold holds, proceeds to step S760.

At step S730, the M component density value Mt and the C component density value Ct are compared with each other. If Ct>Mt holds, the process proceeds to step S740, at which output values by the error diffusion processing of the C and M components are determined.

That is, a common multivalue conversion table for the C and M components as shown in Table 10 is used. First, as the C component output value (C out), a greater one of “1” and f(Ct) value (in multivalue conversion table as a function of a density value Ct) is selected. For example, if f(Ct) is “0”, C out=1 holds; if f(Ct) is “1”, C out=1 holds; and if f(Ct) is “2”, C out=2 holds.

Further, as the M component output value (M out), a value corresponding to the density value Mt is determined by referring to the multivalue conversion table of Table 10, as M out=g(Mt)(in multivalue conversion table as a function of a density value Mt).

TABLE 10 MULTIVALUE OUTPUT DENSITY VALUE 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 10 0 11 0 12 0 13 0 14 0 15 0 16 0 17 0 18 0 19 0 20 0 21 0 22 0 23 0 24 0 25 0 26 0 27 0 28 0 29 0 30 0 31 0 32 0 33 0 34 0 35 0 36 0 37 0 38 0 39 0 40 0 41 0 42 0 43 0 44 0 45 0 46 0 47 0 48 0 49 0 50 0 51 0 52 0 53 0 54 0 55 0 56 0 57 0 58 0 59 0 60 0 61 0 62 0 63 0 64 0 65 0 66 0 67 0 68 0 69 0 70 0 71 0 72 0 73 0 74 0 75 0 76 0 77 0 78 0 79 0 80 0 81 0 82 0 83 0 84 0 85 1 86 1 87 1 88 1 89 1 90 1 91 1 92 1 93 1 94 1 95 1 96 1 97 1 98 1 99 1 100 1 101 1 102 1 103 1 104 1 105 1 106 1 107 1 108 1 109 1 110 1 111 1 112 1 113 1 114 1 115 1 116 1 117 1 118 1 119 1 120 1 121 1 122 1 123 1 124 1 125 1 126 1 127 1 128 1 129 1 130 1 131 1 132 1 133 1 134 1 135 1 136 1 137 1 138 1 139 1 140 1 141 1 142 1 143 1 144 1 145 1 146 1 147 1 148 1 149 1 150 1 151 1 152 1 153 1 154 1 155 1 156 1 157 1 158 1 159 1 160 1 161 1 162 1 163 1 164 1 165 1 166 1 167 1 168 1 169 1 170 2 171 2 172 2 173 2 174 2 175 2 176 2 177 2 178 2 179 2 180 2 181 2 182 2 183 2 184 2 185 2 186 2 187 2 188 2 189 2 190 2 191 2 192 2 193 2 194 2 195 2 196 2 197 2 198 2 199 2 200 2 201 2 202 2 203 2 204 2 205 2 206 2 207 2 208 2 209 2 210 2 211 2 212 2 213 2 214 2 215 2 216 2 217 2 218 2 219 2 220 2 221 2 222 2 223 2 224 2 225 2 226 2 227 2 228 2 229 2 230 2 231 2 232 2 233 2 234 2 235 2 236 2 237 2 238 2 239 2 240 2 241 2 242 2 243 2 244 2 245 2 246 2 247 2 248 2 249 2 250 2 251 2 252 2 253 2 254 2 255 2

Further, if Ct≦Mt holds, the process proceeds to step S750, at which the common multivalue conversion table for the C and M components shown in the Table 10 is referred to, and the output values from the error diffusion processing of the C and M components are determined.

That is, as the C component output value (C out), a value corresponding to the density value Ct is determined by referring to the multivalue conversion table of Table 10, as C out=f(Ct), and as the M component output value (M out), a greater one of “1” and g(Mt) value (in multivalue conversion table as a function of a density value Mt) is selected.

Further, at step S760, the common multivalue conversion table for the C and M components shown in the Table 10 is referred to, then, as the C component output value (C out), a value corresponding to the density value Ct is determined by referring to the multivalue conversion table in Table 10, as C out=f(Ct), and as the M component output value (M out), a value corresponding to the density value Mt is determined by referring to the multivalue conversion table of Table 10, as M out=g(Mt).

After steps S740 and S750 or S760, the process ends.

Note that in this embodiment, “85” is used as the threshold value (Threshold).

FIG. 23 is a diagram showing threshold conditions regarding the C and M components in the processing shown in FIG. 22.

Further, in the present embodiment, for the sake of simplification of explanation, a common table is used as the multivalue conversion tables f(Ct) and g(Mt), however, the common table is not necessarily used but separate tables may be used.

Further, Table 10 merely has density values 0 to 255, however, as actual density values Ct and Mt may have density variation widths, which may differ in accordance with conditions of multivalue conversion means and error diffusion method, about −128 to +383 at the maximum, the present invention is not limited to the values shown in Table 10. In the present embodiment, although the following values are not included for the sake of simplification of explanation, actually unshown Ct(Mt) table part of “0” or less may have the same values of those in the Ct(Mt)=0 multivalue conversion table, and unshown Ct(Mt) table part of “255” or more may have the same values of those in the Ct(Mt)=255 multivalue conversion table.

Note that in the present embodiment, only ternarization is handled, however, if the ink-jet printer as the image output device is capable of handling quaternary or quinary representation by using drop modulation and same-color various density ink (e.g. thin cyan ink, thick cyan ink, thin magenta ink and thick magenta ink), threshold tables for multivalue error diffusion processing such as quaternarization or quinarization may be generated.

Accordingly, in the above-described embodiment, even in conversion of multivalued image data into N-ary code, as the processing is performed by using a predetermined format threshold table, even if the threshold conditions are complicated, the processing can be performed in a simple manner, and as the processing is simple, the complicated threshold conditional process can be performed at a high speed.

Note that in the above embodiments, the liquid discharged from the printhead has been described as ink, and the liquid contained in the ink tank has been described as ink. However, the liquid is not limited to ink. For example, the ink tank may contain processed liquid or the like discharged to a print medium to improve fixability or water repellency of a printed image or to increase the image quality.

The embodiments described above have exemplified a printer, which comprises means (e.g., an electrothermal transducer, laser beam generator, and the like) for generating heat energy as energy utilized upon execution of ink discharge, and causes a change in state of an ink by the heat energy, among the ink-jet printers. According to this ink-jet printer and printing method, a high-density, high-precision printing operation can be attained.

As the typical arrangement and principle of the ink-jet printing system, one practiced by use of the basic principle disclosed in, for example, U.S. Pat. Nos. 4,723,129 and 4,740,796 is preferable. The above system is applicable to either one of the so-called on-demand type or a continuous type. Particularly, in the case of the on-demand type, the system is effective because, by applying at least one driving signal, which corresponds to printing information and gives a rapid temperature rise exceeding nucleate boiling, to each of electrothermal transducers arranged in correspondence with a sheet or liquid channels holding a liquid (ink), heat energy is generated by the electrothermal transducer to effect film boiling on the heat acting surface of the printhead, and consequently, a bubble can be formed in the liquid (ink) in one-to-one correspondence with the driving signal. By discharging the liquid (ink) through a discharge opening by growth and shrinkage of the bubble, at least one droplet is formed. If the driving signal is applied as a pulse signal, the growth and shrinkage of the bubble can be attained instantly and adequately to achieve discharge of the liquid (ink) with the particularly high response characteristics.

As the pulse driving signal, signals disclosed in U.S. Pat. Nos. 4,463,359 and 4,345,262 are suitable. Note that further excellent printing can be performed by using the conditions described in U.S. Pat. No. 4,313,124 of the invention which relates to the temperature rise rate of the heat acting surface.

As an arrangement of the printhead, in addition to the arrangement as a combination of discharge nozzles, liquid channels, and electrothermal transducers (linear liquid channels or right angle liquid channels) as disclosed in the above specifications, the arrangement using U.S. Pat. Nos. 4,558,333 and 4,459,600, which disclose the arrangement having a heat acting portion arranged in a flexed region is also included in the present invention. In addition, the present invention can be effectively applied to an arrangement based on Japanese Patent Laid-Open Publication No. 59-123670 which discloses the arrangement using a slot common to a plurality of electrothermal transducers as a discharge portion of the electrothermal transducers, or Japanese Patent Laid-Open No. 59-138461 Publication which discloses the arrangement having an opening for absorbing a pressure wave of heat energy in correspondence with a discharge portion.

Furthermore, as a full line type printhead having a length corresponding to the width of a maximum printing medium which can be printed by the printer, either the arrangement which satisfies the full-line length by combining a plurality of printheads as disclosed in the above specification or the arrangement as a single printhead obtained by forming printheads integrally can be used.

In addition, an exchangeable chip type printhead which can be electrically connected to the apparatus main body and can receive ink from the apparatus main body upon being mounted on the apparatus main body can be employed as well as a cartridge type printhead in which an ink tank is integrally arranged on the printhead itself as described in the above embodiments.

It is preferable to add recovery means for the printhead, preliminary auxiliary means and the like to the above-described construction of the printer of the present invention since the printing operation can be further stabilized. Examples of such means include, for the printhead, capping means, cleaning means, pressurization or suction means, and preliminary heating means using electrothermal transducers, another heating element, or a combination thereof. It is also effective for stable printing to provide a preliminary discharge mode which performs discharge independently of printing.

Furthermore, as a printing mode of the printer, not only a printing mode using only a primary color such as black or the like, but also at least one of a multi-color mode using a plurality of different colors or a full-color mode achieved by color mixing can be implemented in the printer either by using an integrated printhead or by combining a plurality of printheads.

Moreover, in each of the above-mentioned embodiments of the present invention, it is assumed that the ink is a liquid. Alternatively, the present invention may employ an ink which is solid at room temperature or less and softens or liquefies at room temperature, or an ink which liquefies upon application of a use printing signal, since it is a general practice to perform temperature control of the ink itself within a range from 30° C. to 70° C. in the ink-jet system, so that the ink viscosity can fall within a stable discharge range.

In addition, in order to prevent a temperature rise caused by heat energy by positively utilizing it as energy for causing a change in state of the ink from a solid state to a liquid state, or to prevent evaporation of the ink, an ink which is solid in a non-use state and liquefies upon heating may be used. In any case, an ink which liquefies upon application of heat energy according to a printing signal and is discharged in a liquid state, an ink which begins to solidify when it reaches a printing medium, or the like, is applicable to the present invention. In this case, an ink may be situated opposite electrothermal transducers while being held in a liquid or solid state in recess portions of a porous sheet or through holes, as described in Japanese Patent Laid-Open Publication No. 54-56847 or 60-71260. In the present invention, the above-mentioned film boiling method is most effective for the above-mentioned inks.

In addition, the ink-jet printer of the present invention may be used in the form of a copying machine combined with a reader and the like, or a facsimile apparatus having a transmission/reception function in addition to an image output terminal of an information processing apparatus such as a computer.

The present invention can be applied to a system constituted by a plurality of devices (e.g., a host computer, an interface, a reader and a printer) or to an apparatus comprising a single device (e.g., a copy machine or a facsimile apparatus).

Further, the object of the present invention can be also achieved by providing a storage medium (or recording medium) storing software program code for performing the aforesaid processes to a system or an apparatus, reading the program code with a computer (e.g., CPU, MPU) of the system or apparatus from the storage medium, then executing the program. In this case, the program code read from the storage medium realizes the functions according to the embodiments, and the storage medium storing the program code constitutes the invention. Furthermore, besides aforesaid functions according to the above embodiments are realized by executing the program code which is read by a computer, the present invention includes a case where an OS (operating system) or the like working on the computer performs a part or entire processes in accordance with designations of the program code and realizes functions according to the above embodiments.

Furthermore, the present invention also includes a case where, after the program code read from the storage medium is written in a function expansion card which is inserted into the computer or in a memory provided in a function expansion unit which is connected to the computer, CPU or the like contained in the function expansion card or unit performs a part or entire process in accordance with designations of the program code and realizes functions of the above embodiments.

As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims. 

1. An image processing apparatus for performing error diffusion processing on multi-valued image data comprised of plural color components including a first color component and a second color component, comprising: a generation unit configured to generate values of the first and second color components for a pixel of interest from multi-valued image data of the first and second color components representing the pixel of interest and multi-valued image data of the first and second color components error-diffused to the pixel of interest; a binarization unit configured to binarize the values of the first and second color components for the pixel of interest generated by said generation unit; and an image formation unit configured to form an image based on a result of the binarization, wherein said binarization unit binarizes the values of the first and second color components: (1) in a case where a sum of the values of the first and second color components is less than a predetermined threshold value, such that neither a dot of the first color component nor a dot of the second color component is formed by said image formation unit; (2) in a case where the sum of the values of the first and second color components is greater than the predetermined threshold value and one of the values of the first and second color components is equal to or less than the predetermined threshold value, such that only a dot of one of the first and second color components having a greater value than that of the other of the first and second color components is formed by said image formation unit; and (3) in a case where the sum of the values of the first and second color components is greater than the predetermined threshold value and both of the values of the first and second color components are greater than the predetermined threshold value, such that both dots of the first and second color components are formed by said image formation unit.
 2. The apparatus according to claim 1, wherein said binarization unit includes: a first comparison unit configured to compare the sum of the values of the first and second color components with the predetermined threshold value; a second comparison unit configured to compare the value of the first color component with that of the second color component so as to discriminate which one is greater than the other; a third comparison unit configured to compare the value of the first color component with the predetermined threshold value; and a fourth comparison unit configured to compare the value of the second color component with the predetermined threshold value.
 3. The apparatus according to claim 1, wherein the plural color components are a yellow component, a magenta component, a cyan component and a black component, and the first color component is the cyan component, and the second color component is the magenta component.
 4. The apparatus according to claim 1, wherein said image formation unit is an ink-jet printer.
 5. The apparatus according to claim 1, wherein the predetermined threshold value is approximately half of a maximum value of each color component.
 6. An image processing method for performing error diffusion processing on multi-valued image data comprised of plural color components including a first color component and a second color component and outputting a result of the image processing to an image formation apparatus, comprising: a generation step of generating values of the first and second color components for a pixel of interest from multi-valued image data of the first and second color components representing the pixel of interest and multi-valued image data of the first and second color components error-diffused to the pixel of interest; and a binarization step of binarizing the values of the first and second color components for the pixel of interest generated at said generation step, wherein said binarization step binarizes the values of the first and second color components: (1) in a case where a sum of the values of the first and second color components is less than a predetermined threshold value, such that neither a dot of the first color component nor a dot of the second color component is formed by said image formation apparatus; (2) in a case where the sum of the values of the first and second color components is greater than the predetermined threshold value and one of the values of the first and second color components is equal to or less than the predetermined threshold value, such that only a dot of one of the first and second color components having a greater value than that of the other of the first and second color components is formed by said image formation apparatus; and (3) in a case where the sum of the values of the first and second color components is greater than the predetermined threshold value and both of the values of the first and second color components are greater than the predetermined threshold value, such that both dots of the first and second color components are formed by said image formation apparatus.
 7. A computer readable memory medium on which is stored a computer executable a program that, when executed by a computer performs an image processing method for performing error diffusion processing on multi-valued image data comprised of plural color components including a first color component and a second color component and outputting a result of the image processing to an image formation apparatus, comprising: a generation step of generating values of the first and second color components for a pixel of interest from multi-valued image data of the first and second color components representing the pixel of interest and multi-valued image data of the first and second color components error-diffused to the pixel of interest; and a binarization step of binarizing the values of the first and second color components for the pixel of interest generated at said generation step, wherein said binarization step binarizes the values of the first and second color components: (1) in a case where a sum of the values of the first and second color components is less than a predetermined threshold value, such that neither a dot of the first color component nor a dot of the second color component is formed by said image formation apparatus; (2) in a case where the sum of the values of the first and second color components is greater than the predetermined threshold value and one of the values of the first and second color components is equal to or less than the predetermined threshold value, such that only a dot of one of the first and second color components having a greater value than that of the other of the first and second color components is formed by said image formation apparatus; and (3) in a case where the sum of the values of the first and second color components is greater than the predetermined threshold value and both of the values of the first and second color components are greater than the predetermined threshold value, such that both dots of the first and second color components are formed by said image formation apparatus. 